1. Field of the Invention
The invention relates to an injection arrangement having an actuator for needle stroke control, in order to achieve a variable opening pressure of the nozzle needle. Such injection arrangements are preferentially used in fuel injection systems of internal combustion engines in motor vehicles
2. Prior Art
From European Patent Disclosure EP 0 823 549 A2, an injector for an injection system in internal combustion engines is known. In the injector housing of this industrial embodiment, two control valves located one after the other are provided, triggered by a magnet. The triggering of one of the two valves necessarily causes the actuation of the further valve. The advantage of this embodiment is the pressure compensation of the needle control valve in all operating states; the disadvantage of this embodiment is that decoupling of the reciprocation events of the two in-line valves is not possible with embodiment of EP 0 823 549 A2. This in turn limits the possibilities for varying the injection pressure course considerably. With the embodiment of EP 0 823 549 A2, it is difficult to achieve an adaptation of the injection pressure course to individual requirements for certain designs of internal combustion engines.
By the triggering of the control valves in the injector by a piezoelectric actuator, while avoiding magnet valves that take up installation space, very fast valve switching times can be attained by means of piezoelectric actuators. This has an especially favorable effect at relatively high rpm, at which the available time for combustion becomes less and less anyway, and the accurate formation of the injection pressure course definitively affects the course of combustion. Another advantage is the substantially more-compact structural shape that can be attained by using a piezoelectric actuator and that becomes possible by means of an offset disposition of the control valve and actuator. Thus greater freedom of design is available for the geometric design of an injector of this kind.
The decoupling of the two control valves provided in the injector housing from one another also makes it possible to produce the components at less expense. No added production variations are created, so that the production tolerances can have a tendency to be widened, which favorably affects the production costs for the components. Also because of the widening of the production tolerances, the range of deviation of individual examples of a given injector in one production batch can be reduced. The leakage losses during the injection event are completely suppressed; a leakage loss occurs only during the pressure buildup phasexe2x80x94when the nozzle needle is supposed to remain closed.
The injection arrangement of the present invention allows a variation of the opening pressure of the nozzle needle for the preinjection phase, main injection phase, and optionally a postinjection phase that may be required. A postinjection at an elevated pressure level is possible by means of the pressure compensation system at one of the control valves. Depending on how a throttle element, which is assigned to a nozzle needle spring chamber that acts on the nozzle needle, is designed, the absolute highest pressure established toward the end of the main injection upon further triggering of one of the two control valves can be specified in a targeted way, as can the course of the pressure increase up to the highest value.